sunxi: kconfig: Add top-level ARCH_SUNXI

And make TARGET_SUN[45678]I a choice variable under this.

configs updated with:
    sed -i -e 's/^\(\+S:\)\?CONFIG_TARGET_SUN.I=y/\1CONFIG_ARCH_SUNXI=y\n&/g' configs/*

Signed-off-by: Ian Campbell <ijc@hellion.org.uk>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
diff --git a/configs/Mele_M3_defconfig b/configs/Mele_M3_defconfig
index a043ad2..2493446 100644
--- a/configs/Mele_M3_defconfig
+++ b/configs/Mele_M3_defconfig
@@ -4,4 +4,5 @@
 +S:CONFIG_MMC_SUNXI_SLOT_EXTRA=2
 +S:CONFIG_MMC0_CD_PIN="PH1"
 +S:CONFIG_ARM=y
++S:CONFIG_ARCH_SUNXI=y
 +S:CONFIG_TARGET_SUN7I=y